In fuel injection and modern carburetor systems in internal combustion engines, it is advantageous to block the supply of fuel to the engine during overrun operation of the vehicle in order to reduce fuel consumption and pollutant emissions. The vehicle is in overrun operation when the throttle valve is substantially closed (i.e., the accelerator pedal is in an idle position) and the instantaneous rotational speed of the engine is greater than a predetermined threshold value.
German Published Patent Application No. 32 10 512 shows a system in which the fuel supply to the engine is blocked only above a certain temperature. The measured temperature is the temperature of the engine intake air and/or the temperature of the surroundings of the engine. The system is based on the assumption that low temperatures can be indicative of snow and ice-covered roadways. In low temperatures, the reduction in rotational speed of the engine caused by the blockage of fuel can be disadvantageous, because the relatively large ("braking") force exerted on the vehicle's driving wheel(s) by the engine, which results from the reduced rotational speed of the engine, resists rotation of the vehicle's driving wheel(s) and, hence, increases the danger of sliding or skidding.
One disadvantageous of this system, however, is that because the cutting-off (limiting) of the flow of fuel to the engine during overrun operation of the vehicle takes place only during the warm seasons, which can be a considerable time period during the year, there is a corresponding increase in fuel consumption.
German Patent No. DE-OS 38 08 692 shows a system in which the braking moment is limited during thrust which the injection of fuel to the engine is controlled as a function of engine speed and time, in order to limit the braking force, during overrun operation, to a value which is sufficiently low to ensure that the driving wheels will not be locked. A plot of the fuel injection quantity as a function of time has a ramp shape, which may be influenced by parameters indicative of the operating condition of the engine, such as engine temperature, engine speed, and the gear in which the vehicle is operating.
A method for recognizing whether the vehicle is moving along a substantially straight or curved path ("curved path recognition") is described in International Patent Application No. WO 89/04782. The differences between velocity signals from diagonally opposite wheels, and signals indicative of the time variation of these differences are generated. If one of these signals exceeds a specified threshold value, then a curved path recognition signal is emitted.
It is an object of the present invention to overcome the problems and disadvantages of known methods for controlling the flow of fuel to the engine during overrun operation.